The present invention generally relates to the adhesiveless laser welding of two nonmetallic materials, preferably but not necessarily and, more particularly, to the laser welding of two materials using an optical fiber that holds the materials in contact while directing a laser emission to the pattern area to be welded.
Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Alternatively, a piezoelectric element may be used to eject a droplet of ink through an associated orifice onto the paper. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper.
An inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each ejection chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of ink ejection elements, one ejection element per ink ejection chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper. Alternatively, a piezoelectric element may be used to eject a droplet of ink through an associated orifice onto the paper.
In U.S. application Ser. No. 07/862,668, filed Apr. 2, 1992, entitled xe2x80x9cIntegrated Nozzle Member and TAB Circuit for Inkjet Printhead,xe2x80x9d a novel nozzle member for an inkjet print cartridge and method of forming the nozzle member are disclosed. This integrated nozzle and tab circuit design is superior to the orifice plates for inkjet printheads formed of nickel and fabricated by lithographic electroforming processes. A barrier layer formed on the substrate includes ejection chambers, surrounding each orifice, and ink flow channels which provide fluid communication between a ink reservoir and the ejection chambers. A flexible tape having conductive traces formed thereon has formed in it nozzles or orifices by Excimer laser ablation. By providing the orifices in the flexible circuit itself, the shortcomings of conventional electroformed orifice plates are overcome. The resulting nozzle member having orifices and conductive traces may then have mounted on it the substrate and barrier layer containing ink ejection elements associated with each of the orifices. Additionally, the orifices may be formed aligned with the conductive traces on the nozzle member so that alignment of electrodes on a substrate with respect to ends of the conductive traces also aligns the ejection elements with the orifices. The leads at the end of the conductive traces formed on the back surface of the nozzle member are then connected to the electrodes on the substrate and provide energization signals for the ejection elements. The above procedure is known as Tape Automated Bonding (xe2x80x9cTABxe2x80x9d) of an inkjet printhead assembly, or TAB Head Assembly, (hereinafter referred to as a xe2x80x9cTHAxe2x80x9d)
An existing solution for attaching a nozzle member having orifices to a substrate, containing ink ejection chambers and ink ejection elements, is to adhesively affix the top surface of the substrate""s barrier layer to the back surface of the flexible circuit using a thin adhesive layer, such as an uncured layer of poly-isoprene photoresist, applied to the top surface of the barrier layer. A separate adhesive layer may not be necessary if the top of the barrier layer can be otherwise be made adhesive. The resulting substrate structure is then positioned with respect to the back surface of the flexible circuit so as to align the ink ejection chambers with the orifices formed in the flexible circuit. After the above-described preliminary adhesively-affixing step and the previously mentioned electrical-lead TAB bonding step, the aligned and bonded substrate and flexible circuit structure is then heated while applying pressure to cure the adhesive layer and firmly affix the substrate structure to the back surface of the flexible circuit.
The heat and pressure step utilizes an aluminum plate having a relatively malleable rubber shoe secured to the bottom surface of the aluminum plate. The heat and pressure step provides a downward force on the aluminum plate while applying heat to the substrate in order to affix the flexible tape to the top surface of the barrier layer. The rubber shoe extends over the edges of the substrate, and the downward force causes the tape to bend where not supported by the barrier layer or substrate. Due to the bending of the tape, the resulting TAB head assembly has nozzles which are skewed with respect to the substrate causing ink trajectory errors. Thus, when the TAB head assembly is scanned across a recording medium, the TAB head assembly trajectory errors will affect the location of printed dots and thus affect the quality of printing.
Nozzle skewing is caused by lamination pressure and the semifluid properties of the polymeric barrier material at temperatures higher than its glass transition temperature when heated. Delamination of the nozzle member from the barrier layer is caused by the post-bonding stress in the barrier layer. During the lamination process, the barrier material between the adjacent vaporization chambers is under pressure and is compressed erratically, which causes sloping of the nozzle member surface. A subsequent baking process releases stress in the barrier created by the bonding process, increasing nozzle skewing, and causes delamination. In a combined effect, skewing may also be caused by the evaporation of some volatile components in the barrier material and hence the barrier material and hence the barrier shrinkage at the exposed boundaries in the prolonged baking process. Delamination both at THA level and pen level are caused by the weak adhesive interface between the substrate and the flexible tape.
In addition, the barrier material and adhesion degrades with the aggressive solvents in newer ink formulations. Moreover, all workable solutions developed for THA to print cartridge body detachment problems caused by the stresses involved in the THA to print cartridge body attachment process, resulted in increased delamination at the adhesive substrate/tape interface.
Accordingly, it would be advantageous to have an improved printhead design for facilitating the attachment of a nozzle member to the substrate which increases the substrate/tape interface bond strength and reduces deformation of the barrier material, ink trajectory errors, detachment and delamination.
This in turn would result in ease of assembly, higher yields, improved reliability, ease of surface serviceability, and overall material and manufacturing cost reductions.
The present invention provides a method of laser welding of two materials by a laser beam having a specified wavelength, comprising the steps of providing a first material with a seed metal pattern on a surface thereof and a second material with a corresponding mating seed metal pattern on a surface thereof, said seed metal having a suitable absorption at the wavelength of the laser beam; aligning the seed metal pattern on the surface of the first material and the corresponding mating seed metal pattern on the surface of a second material; holding the mating seed metal patterns in contact at a bond surface with an optical fiber; and laser welding the seed metal patterns by directing the laser beam through the optical fiber.
The present invention provides a method for the solderless laser welding of two materials by using a laser light beam attached to a fiber optic system which directs the light to a to create a seam weld. The phrases xe2x80x9cthrough bulk materialxe2x80x9d and xe2x80x9cthrough bulk substancexe2x80x9d, appearing in certain of the appended claims with regard to the path of the laser beam, are used to make plain that in the invention recited in those particular claims the beam is propagating through the material itself (of, e.g., a TAB tape or other component), not through a window therein. By using a fiber optic system the laser beam is optimally converted into thermal energy and weld flaws due to underheating or destruction of the materials due to overheating does not occur. The method and apparatus provide rapid, reproducible laser welding even for the smallest of contact geometries. For example, the method of the invention results in solderless gold-to-gold compression laser welding of a silicon substrate to the material contained in a polymer flex circuit tape, such as a polyimide, without damaging the tape. A strong solderless gold-to-gold bond can be formed between a gold bond line, or complex weld seam pattern on the flex circuit tape and a mating gold bond line or weld seam pattern on a semiconductor chip without any damage to the tape and prevents delamination and nozzle skewing associated with the adhesive curing process of other methods. The reduced nozzle skewing provides less dot placement error for print cartridges, and therefore better print quality.
The present invention provides an improved printhead design for facilitating the attachment of a nozzle member to the substrate, which increases nozzle area stiffness and nozzle camber angle and directionality, the substrate/tape interface bond strength and reduces deformation of the nozzle member, which provides higher consistent ink chamber refill speeds, and reduces ink trajectory errors and delamination. In addition, in particular embodiments the invention provides increased tolerance to aggressive solvents in inks and more consistent chamber geometry resulting in better control over drop volume. The invention improves the quality, repeatability and reliability of the pen and results in less process steps, thereby improving processing time, cost and reduced in-process handling.
The above in turn results ease of assembly, higher yields, improved reliability, ease of nozzle serviceability, and overall material and manufacturing cost reduction:
While the present invention will be described, for purposes of illustration only, in conjunction with the laser welding of a TAB circuit to the silicon substrate of an inkjet printhead, the present method and apparatus for the solderless laser welding of two contact materials by using a laser light beam attached to a fiber optic system is applicable to laser welding other materials to each other.
Other advantages will become apparent after reading the disclosure.